Method and devices for producing naphthalene from coke produced from coke oven crude gas

ABSTRACT

The invention relates to a method for producing naphthalene from coke oven crude gas. The coke oven crude gas is directly cooled by means of sprinkling water thereon, and the naphthalene is obtained by subsequent refrigerating and treatment. The invention is characterised in that after direct cooling, the coke oven crude gas is then guided through an electrofiler to be subsequently cooled in such a manner that the naphthalene contained in the coke oven crude gas is separated from the gaseous phase and is obtained in the form of pure naphthalene without any additional treatment.

[0001] The invention relates to a method of recovering naphthalene fromcoke oven crude gas according to the preamble of claim 1 as well asapparatus suitable for that purpose.

[0002] In the thermal treatment of coal under the exclusion of air in acoke oven, coke oven crude gas is produced which is cooled by means ofwater droplets [trickling water] in a crude gas condenser to about 80°C. and is saturated with water vapor. As a result, about 20% of thenaphthalene entrained with the coke oven crude gas is bound up in tar inthe liquid phase. The remaining 80% of the naphthalene is then condensedin an indirect crude gascooling together with tarry aqueous componentsin a precooler. This condensate is initially fed to the crude gascondenser, there heated to about 80° C. and supplied to a tar separationin which the separation of crude tar from cooled water is effected. Thenaphthalene contained in the crude tar is recovered from the crude tarin highly expensive processes from a process technology view point.Initially in a distillation of the tar a naphthalinol is produced isthen subjected to crystallization in which the crude naphthalene isdeposited out to recover pure naphthalene, further processes likechemical reactions, (for example with sodium hydroxide and sulfuricacid) are required or the raw naphthalene is distilled again.

[0003] The invention has as its object to provide a method of recoveryof naphthalene from coke oven crude gas as well as to provideappropriate apparatus by which the naphthalene can be recovered in highpurity at low cost in a simple manner and way.

[0004] These objects are achieved with the features of claim 1.

[0005] Further details are found in the features of the dependentclaims.

[0006] According to the invention, the crude gas coming from the cokeoven is cooled as is customary with the aid of sprinkling water thereonin the crude gas condenser directly to about 80° C. This results in aliquid phase and a gas phase. The liquid phase is fed to tar separationin which the separation into tar and coal water is effected. A part ofthe coal water is again used for the direct crude gas cooling as thetrickling water. The gaseous phase is fed through an electrostaticfilter in which the solids content and tar content of the coke ovencrude gas is reduced at a temperature of about 80° C. by 99.99%.

[0007] Since the deposition in the electrostatic filter is carried outat a temperature of about 80° C., the naphthalene (predominantly in thegaseous form) remains in the coke oven crude gas after passing theelectrostatic filter. The coke on crude gas is then cooled from about80° C. to about 20° C. such that the naphthalene contained in the crudegas deposits out. Since the solids as well as the tar has already beendeposited in the electrostatic filter, the naphthalene here is a verypure naphthalene which is a saleable product which can be delivereddirectly to the consumer.

[0008] So that the naphthalene in the electrostatic filter will notseparate out, the electrostatic filter is isolated or even heated sothat the isothermal commands in the electrostatic filter will bemaintained at about 80° C. The tar which has been separated out [in theelectrostatic filter] according to the invention serves to protect theinner surfaces of the electrostatic filter from corrosion, theelectrostatic filter can be composed of simple 10 structural steel (forexample: ST 37-3).

[0009] The tar deposited in the electrostatic filter is especially lowin naphthalene since, as has been observed above, the naphthaleneremains in the coke oven gas. This low naphthalene tar is supplied to atar separation stage. Based upon the low naphthalene content (about 2%residual naphthalene content), emulsion formation in the tar-waterseparation is reduced and the tar separation improved. In addition, theresidence time required for the tar-water separation is also reduced.The tar water separation can also be carried out at a somewhat lowertemperature since the emulsion formation is reduced.

[0010] According to a variant of the process, it is also possible tofeed the low naphthalene tar from the electrostatic filter, since it isclose to water free, not to the tar separation stage but directly to thetar storage receptacle. This relieves load on the tar separation stage.The low naphthalene tar can also be stored in a separate tar storagereceptacle and used for other processes like, for example, precoolerflushing.

[0011] The naphthalene can be recovered from the crude gas downstream ofthe electrostatic filter by direct or indirect cooling.

[0012] In the direct cooling, the coke oven crude gas is directly cooledwith water downstream of the electrostatic filter.

[0013] The naphthalene is thereby separated out and is then separatedfrom the water. Since the water is approximately free from impurities,it can be fed in a circulation with corresponding recooling. Therecooling of the circulated water can be effected directly orindirectly. The excess water is supplied to the condenser.

[0014] With indirect cooling the naphthalene crystallizes on the coolingsurfaces.

[0015] The naphthalene which is crystallized out can be recovered bydifferent techniques and in various ways: One possibility is to recoverthe naphthalene by heating. The heating can be effected directly orindirectly. The cooling surfaces can be heated by a heating medium, bothon the “naphthalene side” and also upon the other side and thenaphthalene thus removed and transported through heated conduits to theshipment point.

[0016] The heating can be effected also by heating rods which can bebuilt into the apparatus at appropriate locations.

[0017] Another possibility is to flush the naphthalene with previouslyheated liquid naphthalene. Liquid naphthalene can also be used for theindirect heating.

[0018] It is also possible to dissolve the crystallized-out naphthalenewith a solvent from the cooling surfaces and then to recover it from thesolvent.

[0019] The recovery of the crystallized-out naphthalene can also beeffected mechanically, for example, with the aid of a shaver. Either theshaver or the cooling surface is moved to recover the naphthalene.

[0020] It is also possible to recover the crystallized-out naphthalenewith the aid of mechanical vibrations which can be produced by animpactor or shaker or with the aid of an imbalanced motor.

[0021] In the aforedescribed method the recovery of naphthalene iscarried out discontinuously, that is in a first method step thenaphthalene is crystallized out and in a second method step thecrystallized-out naphthalene is recovered.

[0022] It is however also possible to carry out the recovery ofnaphthalene continuously or quasicontinuously. In this mode ofoperation, a device is fed segment wise into the cooling region or intothe naphthalene recovery region. A continuous operation is also possiblewith the use of a shaver or vibration generator.

[0023] For carrying out the method of the invention, it is onlynecessary to have an electrostatic filter and a device appropriate forthe deposition of naphthalene from which the deposited can be recovered.

[0024] For an after-fitting of existing coking plants it is possible toprovide only the electrostatic filter and use the previously providedprecooler.

[0025] If the electrostatic filter is provided downstream from theprecooler, the electrostatic filter can be built into the crude gas pathupstream of the precooler.

[0026] This electrostatic filter can be built into the crude gas pathahead of the precooler. Electrostatic filters following the precoolingare superfluous in the method according to the invention.

[0027] Since existing coke plants as a rule have multiple precoolers,the method can be carried out as follows with the precoolers which havepreviously been provided:

[0028] One group of for example two precoolers is used to crystallizeout the naphthalene. The remaining precoolers run in the usual precooleroperation with tar flushing. In a quasi continuous operation, forexample, one precooler is used to crystallize out the naphthalene andone precooler is used for the naphthalene recovery. With an increase inthe pressure loss in the precooler for naphthalene recovery or with anincrease in the crude gas discharge temperature by a maximum of 2° C.,the crude gas is no longer fed through this precooler but through the[other] precooler which is in standby status following the naphthalenerecovery.

[0029] The naphthalene crystallized out on the cooler tubing isrecovered by heating the tubing up. The cooler tubing can be heated fromthe interior or from the exterior. A combination of internal andexternal heating is however also possible. After the naphthalene hasbeen recovered from the precooler, it is switched over and the precoolercan again be used for crystallizing out of the naphthalene while thenaphthalene is recovered from the other precooler.

[0030] In this mode of operation, a reduced naphthalene recovery can becarried out and a switchover to partial or also complete cooleroperation in the classical manner.

[0031] In this mode of precooler operation it is advantageous to preventthe naphthalene from plugging up the precooler by flushing the precoolerwith the low naphthalene tar from the electrostatic filter.

[0032] With the method according to the invention of recoveringnaphthalene from coke oven crude gas, the apparatus suitable forrecovering naphthalene can use a conventional precooler. In the coolingstep, the naphthalene crystallizes out on the cooling tubing from thegas phase and then the naphthalene is recovered in accordance with theabove described process. During the naphthalene recovery the coke ovencrude gas is lead through the precooler which is in a stand by state.

[0033] The precooler can be equipped for a quasicontinuous naphthalenerecovery. Then the precooler must be equipped segment wise withcontrollable valves. In this manner and way it is possible to carry outsimultaneously in the precooler a cooling operation for crystallizingout the naphthalene and a naphthalene recovery operation with heating upof the naphthalene.

[0034] For the recovery of the naphthalene, other apparatus is alsopossible. It is only necessary that a cooling surface be provided from,which using the above described process, the naphthalene can berecovered. As cooling surfaces for example, a drum or disk can be used.If this drum or these disks are equipped with a shaver, the naphthalenerecovery can also be effected continuously.

[0035] It is also possible to crystallize out the naphthalene in a tubecooler whose tubes are cooled at their outer walls. The naphthalene thendeposits on the tubing inner walls and can be recovered with thedescribed method.

[0036] The aforedescribed and claimed components and those used asdescribed in the examples according to the invention can be selected asto their dimensions, their shapes, their choice of materials and theirtechnological conceptions, without special preconditions so that theycan be employed without limitations in the full range of applications.

[0037] Further details, features and advantages of the subject of theinvention are given in the dependent claims and in the followingdescription relevant to the accompanying drawing in which preferredembodiments of the method of the invention are given by way of exampleand are illustrated.

[0038] The drawing shows:

[0039]FIG. 1 is a schematic illustration of the method for recoveringnaphthalene from coke oven crude gas with direct cooling;

[0040]FIG. 2 is a schematic illustration of the method for recoveringnaphthalene from coke oven crude gas with indirect cooling; and

[0041]FIG. 3 is a schematic illustration of the method variant accordingto which part from the recovery of naphthalene a conventional crude gasfilling can be carried out.

[0042] From FIG. 1 it is seen that a crude gas coming from the coke oven1 is cooled in a crude gas condenser 2 with water droplets supplied by aline 10 from a temperature of about 800° C. to about 80° C. The cokeoven crude gas is fed through an electrostatic filter three in which thesolids and tar content of the coke oven crude gas is reduced by 99.99%.The precipitated tar is fed via a line 7 to the tar separation or to thetar collecting vessel. The coke oven crude gas is fed to a device 4 forseparating out the naphthalene in which the naphthalene is separated outby direct cooling with water and is separated from the water. Thenaphthalene is fed via a line 8 to a separating device which has notbeen shown and in which the naphthalene is separated from residual wateradhering to it. This residual water can be supplied as cooling water.The cooling water is fed in a circulating path through a line 11, acooler 12 and a line 13. Surplus water is fed via a line 9 to the crudegas condenser 2. The coke oven crude gas is fed to a cleaning unit 5where it is freed from hydrogen sulfide, ammonia and optionally formbenzene before it is supplied to a coke oven gas consumer 6.

[0043] In FIG. 2, the process variant with in direct cooling for the forthe recovery of naphthalene has been illustrated. The referencecharacters have the same significance as in FIG. 1. The coke oven crudegas is fed from the electrostatic filter 3 into a device 4 forcrystallizing out the naphthalene and in which the naphthalene isdeposited on the cooling surface while the water vapor which iscondensed out is carried away via the line 9 to the crude gas condenser2. The naphthalene crystallized out on the cooling surfaces is drawn offas liquid naphthalene from the device upon heating of the coolingsurfaces and is transported through a heated duct 8 to a shipmentfacility (not shown).

[0044] In FIG. 3, a process scheme has been shown in which twoprecoolers 4 and 4′ are used for crystallizing out the naphthalene.

[0045] The device 4 is used for naphthalene recovery, that is obtainingthe pure naphthalene as transported by the line 8 to the shipmentfacility. The device 4′ is used in precooler operation. Thelow-naphthalene tar is used in this case for flushing the precooler 4′to prevent blockage by naphthalene. The remaining reference charactershave the same significance as in FIG. 1. Reference Characters 1. CokeOven 2. Condenser 3. Electrostatic Filter 4. Apparatus for cooling 5.Coke Oven Gas Cleaning 6. Coke Oven consumer 7. Line [Conduit] (Tar) 8.Line [Conduit] (Naphthalene) 9. Line [Conduit] (Condensate) 10. Line[Conduit] (Trickling Water) 11. Line [Conduit] (Cooling Water) 12.Cooler 13. Line [Conduit] (Cooling Water Recycle)

1. A method of recovering naphthalene from coke oven crude gas in whichthe crude gas is directly coupled by means of trickling water andthrough subsequent cooling and processing the naphthalene is recovered,characterized in that the coke oven crude gas, after the direct cokeoven crude gas cooling, is conducted through an electrostatic filter andthen so cooled that the naphthalene contained in the coke oven crude gasis precipitated from the gas phase and without further processing isrecovered as pure naphthalene.
 2. The method according to claim 1characterized in that the electrostatic filter is so insulated or heatedthat it operates isothermally.
 3. The method according to claims 1 and 2characterized in that the cooling of the coke oven crude gas followingthe electrostatic filter is a direct cooling.
 4. The method according toclaims 1 and 2 characterized in that the cooling of the coke oven crudegas following the electrostatic filter is an indirect cooling.
 5. Themethod according to claims 1 to 4 characterized in that the separatednaphthalene is recoupled by heating up.
 6. The method according to claim5 characterized in that the heating up is effected indirectly.
 7. Themethod according to claim 5 characterized in that the heating up iseffected indirectly.
 8. The method according to claims 6 and 7characterized in that the heating up is carried out with already heatedliquid naphthalene.
 9. The method according to claims 1 and 2characterized in that the deposited naphthalene is dissolved with asolvent and the solvent is then removed.
 10. The method according toclaim 1 characterized in that the separated out naphthalene ismechanically recovered.
 11. The method according to claims 1 and 2characterized in that the separated out naphthalene is continuouslyrecovered.
 12. An apparatus for carrying out the method according toclaim 1 characterized in that a conventional precooler is used forseparating out the naphthalene.
 13. The apparatus according to claim 12characterized in that heating rods are provided in the precooler. 14.The apparatus for carrying out the method according to claim 1characterized in that a precooler is equipped with controllable valvesin a segmentwise manner.
 15. An apparatus for carrying out the methodaccording to claim 1 characterized in that a cooling surface is providedwith at least one shaver.
 16. The apparatus for carrying out the methodaccording to claim 1 characterized in that a cooled drum equipped withshavers is provided.
 17. An apparatus for carrying out the methodaccording to claim 1 characterized in that a cooled disk equipped withshavers is provided.
 18. An apparatus for carrying out the methodaccording to claim 1 characterized in that a tube cooler is providedwith cooling of the outer walls of the tubes.
 19. An apparatus forcarrying out the method according to claim 1 characterized in that atleast one vibration generator is provided at a cooling surface.